0d619e215e
An agent's memory cap was rendered into its flake (`memoryMaxBytes` → `services.hyperhive.agent.claudeMemoryMaxBytes`), so the closure depended on it and a changed cap reached the JSC heap ceiling and the subagent `MemoryHigh=` only after a rebuild. hive-c0re now writes the effective `MemoryMax=` in bytes to the agent's runtime dir (`/run/hive/memory-max-bytes` inside) in `write_dropins`, from the same value the drop-in gets. The file is removed for `infinity` or a RAM percentage, and left alone when the drop-in is kept. Inside the container, `nix/agent-modules/memory-cap.nix` reads it at boot: an environment generator sets `BUN_JSC_forceRAMSize` (75%) for every unit and `machinectl shell`, `/etc/set-environment` exports it in login shells, and a unit generator writes `MemoryHigh=` (2/3) as a drop-in for `hive-subagent-daemon`. The render drops `memoryMaxBytes`, the agent option is removed (both spellings fail eval with a removal message), and `effective_memory_bytes_from` goes with its only caller. Part of #5081 (slice S0-2).
68 lines
3.1 KiB
Nix
68 lines
3.1 KiB
Nix
# The container's memory cap, read at boot rather than built in, so a changed
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# cap needs no rebuild.
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#
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# The cap is `MemoryMax=` on the host's `container@` unit, which nothing in
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# here can read: `/sys/fs/cgroup/memory.max` reads `max` at every level from
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# inside. hive-c0re writes its byte count to `/run/hive/memory-max-bytes`
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# before every start (`lifecycle::host_config`), and removes the file when the
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# cap is `infinity` or a RAM percentage. Two values are derived from it, and
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# neither is set without the file:
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#
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# - `BUN_JSC_forceRAMSize`, 75% of the cap. Bun/JavaScriptCore, the runtime
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# under claude-code, sizes its heap ceiling off `/proc/meminfo`, which under
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# nspawn is the host's RAM, so without it the heap grows well past the real
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# wall before GC kicks in hard and choom sessions hang. An environment
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# generator hands it to every unit of the container's systemd, `machinectl
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# shell` sessions (`hivectl choom`) included; `/etc/set-environment` exports
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# it in login shells that no unit starts (`nixos-container root-login`).
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# - `MemoryHigh=` on `hive-subagent-daemon`, two thirds of the cap, as a
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# generator drop-in. The daemon spawns nested `claude` sessions as plain
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# children, so its cgroup already is the "all subagents" cgroup. `High`, not
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# `Max`: past it the kernel reclaims hard and the subagents slow down, so the
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# last third stays free for the agent's own turn, but a subagent that needs
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# more still gets it when the container has memory to spare.
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#
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# Tested by `checks.script-test-agent-memory-cap`.
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{ pkgs, ... }:
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let
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# Sets `bytes`, or exits when there is no file or its first line is not a
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# plain byte count. A leading zero would read as octal, and 16 digits or
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# more could overflow `bytes * 75`. Shell builtins only.
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readCap = ''
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bytes=
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[ -r /run/hive/memory-max-bytes ] && read -r bytes < /run/hive/memory-max-bytes
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case "$bytes" in
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"" | 0* | *[!0-9]* | ????????????????*) exit 0 ;;
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esac
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'';
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envGenerator = pkgs.writeShellScript "hyperhive-memory-cap-env" ''
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${readCap}
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printf 'BUN_JSC_forceRAMSize=%s\n' "$((bytes * 75 / 100))"
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'';
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# `$1` is the generator's normal-priority output dir. A drop-in there merges
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# with the unit's own file in /etc.
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unitGenerator = pkgs.writeShellScript "hyperhive-memory-cap" ''
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${readCap}
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dir="$1/hive-subagent-daemon.service.d"
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${pkgs.coreutils}/bin/mkdir -p "$dir"
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printf '[Service]\nMemoryHigh=%s\n' "$((bytes * 2 / 3))" > "$dir/50-memory-high.conf"
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'';
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# Sourced by every shell's `/etc/set-environment`, so POSIX sh only.
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profile = pkgs.writeText "hyperhive-memory-cap.sh" ''
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__hyperhive_cap=$(${envGenerator})
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case "$__hyperhive_cap" in
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BUN_JSC_forceRAMSize=?*) export "$__hyperhive_cap" ;;
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esac
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unset __hyperhive_cap
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'';
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in
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{
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environment.etc."systemd/system-environment-generators/50-hyperhive-memory-cap".source =
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envGenerator;
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systemd.generators.hyperhive-memory-cap = unitGenerator;
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environment.etc."hyperhive/memory-cap.sh".source = profile;
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environment.extraInit = ". /etc/hyperhive/memory-cap.sh";
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}
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